Be₄Si₂O₇(OH)₂

This sample of bertrandite is displayed in the Smithsonian Museum of Natural History. Bertrandite is a silicate of beryllium with the composition Be₄Si₂O₇(OH)₂. The sample at left is about 5 cm across and is from Conselheiro Pena, Minas Gerais, Brazil. The sample is described as bertrandite with elbaite, cookeite and lepidolite.